The USS Ronald Reagan aircraft carrier experienced radiation levels 30 times above normal while its crew conducted disaster relief operations off the coast of Japan in March 2011 after a tsunami damaged reactors at the Fukushima Daiichi Nuclear Power Plant, according to a new analysis[2] published on Monday.

That analysis came just days after 79 Reagan crewmen filed an amended lawsuit[3] in federal court in San Diego against the plant’s operator, Tokyo Electric Power Co. The plaintiffs seek $1 billion in damages, claiming the company was negligent in construction and operation of the plant and during the subsequent meltdown of its reactors following the tsunami March 11, 2011.

Kyle Cleveland, a sociology professor at Temple University Japan, cited transcripts of a conference call between high level Navy and Energy Department officials in an article in the Asia-Pacific Journal, “Mobilizing Nuclear Bias: The Fukushima Nuclear Crisis and the Politics of Uncertainty.” The transcripts, which Cleveland obtained through the Freedom of Information Act, show concern among U.S. officials discussing the level of radioactivity on the Reagan on March 13.

In that transcript, Adm. Kirkland H. Donald, at the time director of naval nuclear propulsion, said the level of radioactivity in the plume emitted from the plant “was probably more significant than what we had originally thought.”